New D800e users (serial no)

Going from a cheap DSLR to a semi-pro DSLR is a significant jump so if you're not seeing a difference in IQ then as you suspected it's due to a lack of experience/skill/etc.

I guess it'd be no different to an average driver getting behind the wheel of an exotic sports car. They wouldn't really appreciate it until they improved their skills.

In the right hands a D800 is a very powerful tool and capable of vastly superior results to a D5100.